RESEARCH ARTICLE Fully Bio-Based Nanocomposite: Formulations For Packaging Application

Adolfo Izzo Renzi Anna Verdoliva Dipartimento di Ingegneria Chimica, dei Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Materiali e della Produzione Industriale, Università di Napoli Federico II. Piazzale Università di Napoli Federico II. Piazzale V.Tecchio, 80, 80125 Napoli, Italy V.Tecchio, 80, 80125 Napoli, Italy [email protected] [email protected]

Giovanni Filippone Domenico Acierno Centro Regionale di Competenza (CRdC) Centro Regionale di Competenza (CRdC) Tecnologie, Università di Napoli Federico II, Tecnologie, Università di Napoli Federico II, Via Nuova Agnano, 11, 80125 Napoli, Italy Via Nuova Agnano, 11, 80125 Napoli, Italy [email protected] [email protected]

INTRODUCTION

The world market of films is dominated high-performance, semi-crystalline with by -based such as low net CO2 emission and global warming potential, terephthalate (PET), polyvinylchloride (PVC), poly- when compared to petroleum based and other ethylene (PE), (PP), (PS) conventional plastics[2,3]. Some of the properties of and polyamide (PA) because of their large availabil- PA11 include high impact and abrasion resistance, low ity at relatively low cost and good mechanical and specific gravity (about 1.03 g/cm3), excellent chemical barrier performances. Environmental concerns are resistance, high thermal stability (melting point of driving the attention of plastic producers towards bio- about 180–190 °C), and ease of processing over a wide , namely polymers obtained from renew- range of processing temperatures (130°C to 240°C). able resources. Among others, poly(lactic acid) Since PA11 is not biodegradable and it is relatively (PLA) is extensively studied because PLA closely expensive compared to other plastic materials includ- resembles polystyrene in terms of high modulus ing petroleum based -6, the aim is minimizing and low elongation to break and poly(ethylene tere- its content in the blend while maintaining it phase con- ) in terms of stiffness and tensile strength tinuity, so as to provide the blend with a PA11 frame- [1,2]. The main drawbacks of PLA are the brittleness work able to resist to high temperatures. This goal is and low heat deflection temperature (HDT), which pursued using small amounts of clay particles, which essentially corresponds to the tem- may simultaneously act as reinforcing nanofiller and perature T~55°C. To overcome these issues we promote the phase continuity of the PA11 phase. propose a strategy that consists in blending PLA with polyamide 11 (PA11), a renewable resource extracted from the castor plant. PA11 is a

Fully Bio-Based Nanocomposite 43 EXPERIMENTAL SECTION 30-60 µm) was estimated by using Totalperm Oxygen, Carbon Dioxide and Water Vapor Permeability Analyser provided by Extrasolution s.r.l., according Materials and blend preparation to ASTM D3985 procedure. The temperature was set The PLA (2002D by Natureworks) has density at 27°C and at Relative Humidity of 0%. The carrier ρ=l.24 g/cm3 at 25°C and melt flow index MFI=6 g/ flow was fixed at 12.3 ml/min and the sample surface l0 min (2l0°C/2.l6 kg). The PA11 (Nylon 11 by Sigma was 2.01 cm2 for each sample. An automatic baromet- Aldrich) has ρ = l.026 g/cm3 at 25°C, glass transition ric compensation was executed by the instrument to set temperature Tg = 46°C and melting temperature Tm the pressure to 1 atm. = l98°C. The is an montmorillonite (OMMT, Thermo gravimetric analysis was carried out on Cloisite 30B from Southern Clay Products) modified a TA Instruments Q500e. Each specimen was heated by 90 meq/l00g of bis(2-hydroxylethyl) methyl tallow from 25°C to 700°C in air with a ramp rate of 20°C/ ammonium cations. The relatively low process- min. The average initial mass of samples was approxi- ing temperature of PAll allows to limit thermal deg- mately 8 mg. radation of PLA during melt blending. In addition, the Dynamic-mechanical analyzes (DMTA) were onset of thermal decomposition of the organic modifier carried out using a Tritec 2000 DMA (Triton technol- in Cloisite 30B is higher than temperature chosen for ogy, UK). The dynamic moduli were measured as a the melt compounding function of temperature in tensile mode at a frequency To minimize phenomena during melt ω=1 Hz and a strain amplitude of 0.005 mm. The mixing, the polymers and the filler were dried at 80°C samples were heated at 3°C/min from ~ -20°C to l20°C. for 12 h in a vacuum oven. The blends were prepared using a Thermo-Haake twin screw extruder at T=210°C RESULTS AND DISCUSSION and screws speed ~80 rpm. The extruded materials were pelletized, dried again and film blown in a second The Young modulus, E, tensile strength, σ , and step using a Collin film blowing line at T=215°C and R elongation at break, εR, of the films are shown in Figure screw speed ~20 rpm. The thickness of the films was 1. typically ranging between 30 and 70 μm. Blending PLA with PA11 results in a decrease of

E and σR with compared to neat PLA, which indicates METHODS poor interfacial adhesion between polymer phases. The addition of only 1%wt of OMMT brings about Mechanical tests were performed according to an enhancement of E and σR, which approach those ASTM D882 method using a dynamometer Tensom- of neat PLA, and a drastic increase of εR. The latter eter 2020 by Alpha Technologies. Rectangular film result suggests that the filler greatly improve the stress specimens of 115 × 10mm were cut using a manual transfer across the polymer-polymer interface. punch cutter. Tensile tests were performed at room The oxygen permeability values are summarizeda) temperature with a cross-head speed of 10mm/min for in Table 2. the first 5mm of elongation and after it was 50 mm/ As far as the barrier properties are concerned, min until the end of the tests. Young modulus, tensile neither blending with PA11 nor the addition of OMMT strength and elongation at break were evaluated in the alter appreciably the oxygen permeability, which extrusion direction on all film sample. remains comparable to that of pure PLA. The results of The oxygen permeability of the films (thickness: TGA analyses are summarized in Table 3, in which the

Journal of Applied Packaging Research 44 Fig.1. a) Young modulus, E and tensile strength, σR, and b) Elongation at break, εR of PLA, PLA/PA11 and PLA/ PA11+OMMT respectively. The error bars represent the standard deviations over x independent measure- ments.

Table 3. Thermogravimetric Parameters of all investi- Table 2. Oxygen Permeability of PLA, PLA/PA11 and gated materials PLA/PA11+OMMT

-9 2 Sample T5%wt Tpeak Sample P’O2 x10 (cm /bar s) PLA 3,79 PLA 324,3 365,2 PLA/PA11 70/30 3,56 PLA/PA11 337,5 365,6 PLA/PA11 70/30 + OMMT 3,80 PLA/PA11 + OMMT 338,8 363,1 PA11 2,58 PA11 416,3 445,8

Table 4. Dynamic-mechanical thermal analyses of PLA, PLA/PA11 and PLA/PA11+OMMT

Sample E’25°C [MPa] E’60°C [MPa] PLA 793 40,8 PLA/PA11 755 62,2 PLA/PA11+OMMT 911 82,1 PA11 1080 550

temperature of incipient thermal degradation (T5%) and and 60°C are reported. the temperature at which the rate of weight loss is the Adding the filler to the blend results in a slight highest (Tpeak) are reported. enhancement of the glassy modulus in the sample PLA/ The onset of thermal degradation of the unfilled PA11+OMMT at 25°C with respect the glassy modulus and filled blends is 15°C higher than neat PLA. This of unfilled blend. This supports the idea that the clay improvement is likely due to the “labyrinth effect” of may exert improve the stress transfer across the inter- the PA11 phase, which acts as an insulating barrier able face[7]. This beneficial effect lasts up to T = 60°C, i.e. to the volatilization process of PLA. The clay does not the glass transition temperature of PLA: the modulus of promote significant improvements[5,6]. the filled blend is twice that of pure PLA. The results of DMTA analyses are summarized in

Table 4. In particular, the storage moduli E’T at 25°C

Fully Bio-Based Nanocomposite 45 CONCLUSION [3] Hu G.S., Wang B.B., Zhou X.M.,2005. “ Compatibility of reactively compatibilized Preliminary characterization of PLA/PA11 polyamide 11 (nylon 11)/polyethylene (PE) blends in the presence of OMMT have demonstrated alloys”. Polymer International, Wiley, Vol. that blending PLA with PA11 results in a decrease 54, Issue 2, pp. 316-319. of E and σ compared to neat PLA, which indicates R [4] Liu T., Lim K. P., Tjiu W. C., Pramoda poor interfacial adhesion between two phases. The K.P., Chen Z. K., 2003. “Preparation and addition of only 1%wt of OMMT brings about an characterization of nylon 11/organoclay enhancement of E and σ , which approach those R nanocomposites”. Polymer, Elsevier, Vol. of neat PLA, and a drastic increase of ε . Neither R 44, Issue 12, pp. 3529-3535. blending with PA11 nor adding the OMMT cause appreciable alterations of the barrier properties of the [5] Wu D., Wu L., Wu L., Zhang M., films, which remains essentially the same as those of 2006.”Rheology and thermal stability of pure PLA blend is 15°C higher than of neat PLA. polylactide/clay nanocomposites”. Polymer This improvement is probably due to the “labyrinth Degradation and Stability, Elsevier, effect” of the PA11 phase. The clay does not promote Volume 91, Issue 12, pp 3149-3155. significant improvements. Finally, the filler brings [6] Russo P., Cammarano S., Bilotti E., about a slight enhancement of the glassy modulus Peijs T., Cerruti P., Acierno D., 2013. compared to the unfilled blend, which suggests that “Physical Properties of Poly Lactic Acid/ the clay may exert some compatibilizing action. Clay Nanocomposite Films: Effect of Such a beneficial effect of the OMMT endures up to Filler Content and Annealing Treatment”. the glass transition of PLA. Journal Of Applied Polymer Science, Wile, Further morphological studies are currently in Vol. 131, Issue 2, pp. 39798-39798. progress to clarify the origin of the improvements [7] [7] Nuzzo A., Acierno D., Filippone of the performances and possibly exploit the filler G., 2012. “Clay-filled bio-based blends of effect. poly(lactic acid) and polyamide 11”. AIP Conference Proceedings, 10-14 June 2012, REFERENCES Ischia, Itala, ISBN: 978-0-7354-1061-9, Vol. 1459, pp 208-210. [1] Dorgan J.R., Lehermeier H., Mang M., 2000. “ Thermal and rheological properties of commercial-grade poly (lactic acid) s”. Journal of Polymers and the Environment, Springer, Vol. 8, Issue 1, pp 1-9. [2] Patel R., Ruehle D. A., Dorgan J. R., Halley P., Martin D., 2014. “Biorenewable blends of Polyammide-11 and Polylactide”. Polymer Engineering & Science, Wiley, Vol. 54, Issue 7, pp 1523-1532.

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